I like Case knives and I own a number of them, though I don’t have a medium Jack.
I have seen some occasional F&F and W&T issues with them, but one advantage of buying from a brick-and-mortar store is that you should be able to handle the actual knife you would be buying prior to purchase to make sure it doesn’t have any of those problems.
I’m not entirely sure if your question is more about Case knives, more about the medium jack pattern, or both. I would say Case generally makes a decent knife. As noted above, I don’t own a medium jack, but the combination of one large and one small blade in a fairly svelte 3 3/8” package that weighs under two ounces should make for a knife that is very pleasant to carry and easily handles any light- to medium-duty pocket knife chores.